98 THE VOYAGE OF H.M.S. CHALLENGER. 



about 31 mm. Colour in spirit yellow. Texture hard and firm owing to the 

 extraordinarily small amount of soft tissues present. Surface almost smooth. Oscula 

 and pores apparently absent. 



Skeleton. — A band of spiculo-fibre forms the axis of the stem or root, and is 

 continued in a looser condition to the summit of the head, there giving rise to the 

 short, slender, projecting, spicular processes already described, each of which is composed 

 of a single large spicule. From the centre of the head bands of spiculo-fibre radiate 

 outwards and downwards, giving rise to the very long spicular processes which fringe 

 the margin of the sponge. At their origin these bands are very broad, but they 

 rapidly taper away to hair-like thinness {vide woodcut, Fig. 5, a'). 



Spicules. — (a) Megasclera ; of one kind only, viz., straight, slender styli, which may 

 attain a length of over 3"5 mm. (b) Mic7-o.sclerct ; (l) anisochelae (PI. XXI. fig. 8) 

 of the usual Cladorhiza type, with the curved shaft much expanded towards the larger 

 end, and with three teeth at each extremity ; length about 0'038 mm. (2) Sigmata 

 (PL XXI. fig. 10), more or less contort, of fair size, and with the ends produced into 

 long, slender, whip-like processes, much as in Cladorhiza ahyssicola, var. co7'tico- 

 cancellata, Carter; length of spicule (from bend to bend) about 0-0756 mm.; these 

 spicules are rather rare. (3) Amphiasters (PL XXI. fig. 9), large and very remarkable 

 spicules, each consisting of a straight shaft with a rosette of five teeth at each end ; 

 these spicules vary considerably in size, reaching about 0'23 mm. in length. They 

 form a very thick, dense layer [vide woodcut. Fig. 5, c), encrusting the entire body, both 

 upper and lower surfaces, and the upper portions of the root and of the long radiating 

 processes. They are confined to this external layer, in which they are very closely 

 packed together without much order. 



As regards external form this species is almost indistinguishable from a species 

 of Cladorhiza obtained at Station 281, which we have called Cladorhiza similis, so 

 that without microscopic examination one would at once put them downi as identical ; 

 microscopic examination, however, shows the spiculation to be widely diff'erent, as will 

 be seen by reference to the description on p. 93. 



We are inclined to regard the presence of extra microsclera (if so they can be 

 called) as a special modification introduced to suit the special requirements of the 

 species, and hence they would be of less value in classification than the ordinary 

 microsclera, the fuU complement of which is also present. The very dense external 

 armature of spicules is doubtless a most efficient protection against the inroads of 

 parasites or other enemies. That allied sponges are subject to such attacks Mall be 

 seen by reference to the description of Cladorhiza longipinna (p. 93). 



Locality. — Station 291, October 27, 1875 ; lat. 39° 13' S., long. 118° 49' W. ; South 

 Pacific ; depth, 2250 fathoms ; bottom, red clay ; bottom temperature, 34°"6. Two 

 good specimens. 



